1. Field of the Invention
The present invention relates to an optical displacement measuring apparatus, especially relates to a small displacement measuring apparatus having a reflection-type scale and a sensor head on which a light emitting device and a light detecting device are mounted.
2. Prior Art
Optical encoders are classified into a reflection-type encoder that detects reflected light from scale gratings, and a transmission-type encoder that detects transmitted light from scale gratings. In these encoders, the reflection type encoder is more advantageous for miniaturizing and thinning than the transmission-type encoder, because a sensor head can be disposed on one side of the scale so as to include both a light emitting portion and a light detecting portion. However, in practice, the reflection-type encoder has such a complicated structure that the sensor head is constructed by combining a substrate on which a light detecting device is mounted, a light emitting device such as an LED, and a print circuit board to which the devices are connected, on an appropriate frame.
Therefore, the conventional reflection-type encoder is too complicated to be formed so as to be installed in a small X-Y table. Further, not only many steps are necessary for assembling the reflecting-type encoder, but also it is difficult to automatize the assembling process and mass-producing process of the encoder.